Motor Insulation Resistance Test Procedure

Curve a shows test values as measured.

Motor insulation resistance test procedure. The insulation resistance tester generally known by its trade name megger is capable of providing critical information regarding the condition of motor insulation. For a three phase motor insulation resistance is usually measured between each motor winding or phase and between each motor phase and motor frame earth using an insulation tester or megger. The measurement of insulation resistance is carried out by means of a megohmmeter high resistance range ohmmeter this is how the test works. Figure 4 typical record of insulation resistance of a mill motor.

Ground insulation test of a motor. Curve b shows same values corrected to 20 c see page 22 giving a definite downward trend toward an unsafe condition. Set the voltage. Insulation resistance test insulation resistance failure of an electric motor is one of the first signs that the motor is about to fail.

Dc voltage of 500 or 1000 v is applied between the windings and the ground of the motor. At a the insulation resistance decreases due to aging and dust accumulation. Historically many field electricians use the somewhat arbitrary standard of 1 megohm per kv. Also acceptable values of insulation resistance depend upon the equipment you re testing.

For a three phase motor the isolation resistance can usually be measured between each motor winding or phase and between each motor stage and motor frame earth by an insulation tester or megger 4. Since 80 of electrical maintenance and testing. The insulation resistance test is the second test required by the electrical safety testing standards. Reverse side of card at right is used to record the test data.

The insulation resistance test consists in measuring the insulation resistance of a. In an industrial facility the recommended procedure is to perform periodic tests and record the results so that damaging trends can be detected and corrected to prevent an outage. Loss of insulation resistance of an electric motor is one of the first signs of motor failure. Regular checks of motor insulation resistance the key to prolonging the life of any electrical device is periodic checks maintenance the insulation resistance of stored and active motors should be checked regularly.

Z 5 date of test r eading in megohms the graph below shows an example of the insulation resistance readings on an electric motor. The international electrical testing association neta specification maintenance testing specifications for electrical power distribution equipment and. Figure 3 typical scale on the megger insulation tester. A if the insulation resistance of a new cleaned or repaired motor that has been stored for some time is less then 10 mω the reason might be that the windings are humid and.